The present invention relates to an integrated field-effect initiator for initiating explosives and, more particularly, to an initiator useful for the ignition or detonation of explosive materials, pyrotechnic materials, propellants, gas generation materials, and the like.
Various devices have been developed for the purpose of initiating explosives; these devices have included exploding conductive wires and foils, spark gaps, and various semiconductor materials. In general, electrical energy is applied to the device and flows through a conductive pathway to generate heat energy that is transferred to a surrounding "first-fire" explosive material. The conductive pathway can be heated to incandescence or vaporized to generate a conductive plasma. In other types of devices, a projectile, known as a "slapper," is positioned immediately adjacent the conductive pathway. The electrical energy conducted through the pathway causes a violent vaporization of the conductive material. Sufficient kinetic energy is transferred to the slapper to ballistically propel the slapper into the "first-fire" material to cause shock waves that start the detonation process.
Historically, a number of disadvantages have been associated with initiators that use a two-terminal, conductive pathway. For example, conductive bridge wires have been susceptible to inadvertent operation from nearby lightening strikes, stray electrical fields from nearby electrical machinery, static electricity, and radio frequency energy from nearby radio transmitters. Semiconductor bridges have been designed to minimize inadvertent discharge and typically include a semiconductor material doped with a selected material to provide desired conduction characteristics, including, for example, a negative temperature coefficient, that provide a measure of immunity from unintended initiation.
Regardless of the type of conductive pathway used, i.e., wires, foils, and semiconductors, initiators are subject to no-fire tests in which the integrity of an initiator is tested by passing an electric current through the conduction pathway at a voltage less than the all-fire value. A typical no-fire test can pass a 500 volt no-fire signal through the initiator in contrast to a 2000 volt all-fire signal. One disadvantage associated with no-fire testing is the heat generated by the conductive pathway as a consequence of the applied no-fire test voltage. The heat, while less than that necessary to effect initiation, is oftentimes sufficient to cause thermal degradation of the "first-fire" material immediately adjacent the conductive pathway. This degradation, which is not easily detectable, can cause a malfunction when the all-fire signal is subsequently applied.